This invention relates generally to the use of magnetic sensors for determining position and direction of a target having magnetic poles and, more particularly, to the use of an array of a plurality of magnetic sensors to determine position and/or direction.
Multiple magnetic sensors have been placed in proximity to a magnetic field from a multi-pole magnet to determine position and direction of a target. For example, a string of Hall effect devices may be used to provide signals that are summed to produce a sine wave that is representative of the average magnetic field over the multi-pole magnet. Summing the signals from the sensor elements in the first half of the Hall string and subtracting the sum of the signals from sensor elements in the second half of the Hall string produces a cosine wave, that is, a sine wave that is 90 degrees out of phase from the sine wave. The sine and cosine waves can then be used to determine the position and direction of a target equipped with the multi-pole magnet.
Such devices are useful in reducing errors in determining position of the target that are due to variations in the magnetic fields or the spacing of the magnetic poles. However, the known devices and methods require the string of sensor devices to have a length that is matched precisely to the pole spacing of the multi-pole magnet with which the magnetic sensors are to be used. In addition, an external magnetic field will bias the magnetic field, e.g., increasing the magnetic North poles and decreasing the magnetic South poles, causing the sine and cosine curves to shift such that the zero points will not be regularly spaced. In either case, the signal processing of the sine and cosine waves produces errors in the position measurement.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.